Generally, a Hall-effect sensor that is a magnetic sensor varies its output voltage in proportional to a magnetic flux density. It is well known that the Hall-effect sensor is widely used in a so-called current sensor or the like which measures the amount of current flowing through a conductor because the Hall-effect sensor can detect the magnetic flux density generated in proportional to the current flowing through the conductor by using characteristics of Hall-effect sensor.
Meanwhile, a so-called hybrid automobile is well known, which uses both an internal combustion engine and a motor as its drive source to reduce exhaust gas and improve fuel saving. Such a hybrid automobile is generally equipped with an inverter device configured to convert DC power supplied from an in-vehicle battery into three-phase AC power. The three-phase AC power converted by the inverter device is supplied to the motor which is a power supply target. Moreover, in such a hybrid automobile, a current sensor is attached to a power-supply conductor, such, for example, as a bus bar or a cable, connecting the motor to a power module, such as an IGBT (insulated gate bipolar transistor), using for in the inverter device. Then, this current sensor is used to detect current flowing through the bus bar or cable, and the inverter device controls power to be supplied to the motor based on the detected current. The current sensor is required to respond within about several microseconds because current to the motor needs to be detected and controlled quick and accurately in order to rotate the motor efficiently.
A conventional current sensor includes, as shown for example in FIG. 1 of Patent Literature 1, a conductor through which current to be detected flows, a magnetic core surrounding the conductor and having an air-gap portion, a Hall-effect sensor placed in the air-gap portion of the core, and a substrate. The motor using for a hybrid automobile or the like undergoes a drastic change in current as large as several hundred amperes, and therefore the magnetic flux density applied to the Hall-effect sensor drastically changes, too. In this regard, if there is an interconnection loop in wire interconnections connecting output electrode pads of the Hall-effect sensor to external terminals or in interconnections on the substrate connecting output external terminals of the Hall-effect sensor to a signal processing circuit such as an amplifier, an induced electromotive force of a measurable magnitude is superimposed on the output voltage. Thus, it is well known to suppress the induced electromotive force superimposed on the output voltage by using a method of routing interconnections on a substrate as described in Patent Literature 1.
As shown in Formula 1, it is well-known that an induced electromotive force is generated in proportional to a time derivative of a magnetic flux density B and an area S of a loop traversed by a magnetic flux.
                              V          induction                =                              -                                          ⅆ                Φ                                            ⅆ                t                                              =                                    -              S                        ⁢                                          ⅆ                B                                            ⅆ                t                                                                        (                  Formula          ⁢                                          ⁢          1                )            (Vinduction: induced electromotive force, Φ: magnetic flux, S: area of loop, and B: magnetic flux density)
In this formula, units are as follows: Vinduction [V], Φ [Wb], S [m2], and B [Wb/m2]. It is needless to say that the unit [V] is equivalent to a unit [Wb/s], and the unit [Wb/m2] is equivalent to a unit [T]
It is needless to say that the induced electromotive force is generated in such a direction that current can flow in a direction cancelling a change in a magnetic field applied to the loop. The output voltage of the Hall-effect sensor undergoes overshoot on the rising edge if the direction of the induced electromotive force has the same polarity as the output voltage, and undergoes undershoot on the rising edge if the direction of the induced electromotive force has an opposite polarity to that of the output voltage. Due to any of these induced electromotive forces, a delay occurs before the output voltage can be outputted stably at a desirable voltage, and such a delay leads to output response delay. Generally, an acceptable tolerance of the overshoot and the undershoot for the current sensor is ±10 of the output voltage in a stable state.
Meanwhile, in recent years, a linear Hall-effect sensor IC in which a Hall-effect sensor and an IC including a signal processing unit for the Hall-effect sensor are sealed in one package, as described for example in Patent Literature 2, has been used in order to reduce the number of components constituting the current sensor to reduce the size thereof. Regarding the linear Hall-effect sensor, it is needless to say that a Hall-effect sensor including a conductive layer made of a compound semiconductor with high sensitivity is of course suitable for the linear Hall-effect sensor, because the higher the sensitivity of the Hall-effect sensor is, the higher the resolution of current detection can be.
It is well known that in the linear Hall-effect sensor IC, a Hall-effect sensor chip made of a compound semiconductor and an IC chip configured to drive the sensor chip and perform signal processing therefor are connected to each other by wire interconnections such as Au wires and are sealed in one package.